1. Field of the Invention
The present invention relates to a process for producing a self-cross-linking alkyl cellulose derivative and a self-cross-linking alkyl cellulose derivative further exhibiting biodegradability which are produced by irradiating a mixture of an alkyl cellulose derivative and water with radioactive rays; and a novel self-cross-linking alkyl cellulose derivative produced through the above process.
2. Background Art
Conventionally, carboxymethyl cellulose (CMC) or salts thereof are employed in the form of aqueous compositions such as paints, adhesives, coating agents, cataplasms, and soft cream; in ground-improving agents in the construction field; and in soil-improving agents, water retention agents, and coating agents in the agricultural and horticultural fields.
Japanese Patent Application Laid-Open (kokai) No. 10-324701 discloses carboxypolysaccharides which are produced chemically through intramolecular or intermolecular self-cross-linking of hyaluronic acid, alginic acid, or CMC (the term “self-cross-linking” refers to cross-linking that proceeds in the absence of a cross-linking agent). According to the method described in this publication, carboxyl and hydroxyl groups of carboxypolysaccharides are subjected to intramolecular or intermolecular dehydration in the presence of a catalyst so as to form ester bonds, whereby self-cross-linking is achieved. This method does not employ radioactive rays to effect cross-linking, and therefore, the preparation of raw materials is complex, and a dehydration catalyst is necessary.
Japanese Patent Application Laid-Open (kokai) Nos. 8-89796 and 8-196901 disclose water-absorbable resins which are produced through chemical cross-linking of carboxyalkyl cellulose or carboxyalkyl starch with amino acids. The cross-linking process according to this publication does not employ radioactive rays, and has some disadvantages that the preparation of raw materials is complex and an expensive cross-linking agent is necessary.
In general, water-soluble polymers are cross-linked by use of a cross-linking agent or under irradiation with radioactive rays, and the resultant polymers are used as highly water-absorbable resins or gelation compounds (simply referred to as “gel”). Particularly, polyacrylic acid is employed as absorbing agents in, for example, paper diapers. However, polyacrylic acid is not biodegradable to any significant extent and has, therefore, associated disposal problems. When such water-absorbable resins or gels are intended to be used in the construction field; i.e., outdoors, they must possess biodegradability after use.
CMC, which is a water-soluble polymer, is known to be biodegradable in the presence of an enzyme such as cellulase. However, when CMC alone is exposed to radioactive rays, CMC is decomposed prior to cross-linking thereof, and thus CMC is not effectively cross-linked through the irradiation.
Japanese Patent Publication (kokoku) No. 47-17965 discloses that CMC can be reacted with epichlorohydrin, to thereby produce a cross-linked product. However, the resultant product exhibits poor water-absorbability and raises problems in terms of safety.